Texaco's search for natural gas or oil in the Chesapeake Bay region came under challenge on two fronts yesterday, as opponents argued that it could wreak environmental havoc in the already stressed estuary.

The Chesapeake Bay Foundation announced at an Annapolis news conference that it is appealing last month's decision by the Maryland Department of Natural Resources to issue Texaco Inc. a permit to drill an exploratory well near Faulkner in Charles County.

Rep. Tom McMillen, D-4th, used the same occasion to say he plans to introduce a bill to prohibit extraction of oil in the Chesapeake region. Texaco also is drilling in Virginia.

"Beginning to drill is the first step in a long process that will change the nature of the Chesapeake Bay," said William C. Baker, bay foundation president.

He said the bay is even more vulnerable to oil spills than Alaska's Prince William Sound, which is still suffering ill effects from the Exxon Valdez spill in 1989.

The bay foundation is asking DNR for a new hearing on the Texaco well permit. Unlike the first hearing, this would be a quasi-legal proceeding at which both sides may present evidence and cross-examine witnesses.

The state must grant such an "adjudicatory" hearing within 30 days if the party requesting it has legal standing to appeal a DNR permit. The Annapolis-based bay foundation has 40,000 members in Maryland and about 300 members in Charles County.

The foundation also wants DNR to hold up Texaco's drilling permit until the appeal is resolved.

Robert Gould, DNR spokesman, said the agency has not received the bay foundation's appeal yet. He would not comment on it until it could be reviewed.

The foundation contends that DNR failed to consider the potential environmental harm that could result from well blowouts or fires, from pipeline breaks or tanker spills if Texaco finds oil or gas.

DNR officials say Texaco's permit only allows exploratory drilling, and the company will have to address such issues before its permit would be modified to allow production.

Deborah Alford, Texaco's spokeswoman, defended its environmental impact assessment, which found that the exploratory well does not threaten the bay or the local environment. She also noted that the company is in the process of drilling its second well in Virginia, where she contended that Texaco has set a "very strong record for operating safely."

Ms. Alford said Texaco expects to find gas, rather than oil, if it finds anything at all.

Mr. Baker said that gas poses fewer environmental hazards than oil, but he noted that Texaco has refused to agree not to pump any oil if any is discovered. And he warned that DNR would be hard-pressed to deny Texaco the right to extract gas or oil once it has invested in exploratory drilling.

The bay foundation's appeal is far from certain. DNR must decide if the environmental group has legal standing to challenge Texaco's permit, an issue for which the foundation's lawyer, Richard H. Mays, said there was little precedent.

Mr. Mays said the foundation may go to court if DNR denies the foundation a hearing or stays Texaco from drilling until the appeal is settled.